The invention relates to a mass spectrometer, more specifically, a mass spectrometer having a flight space wherein ions to be analyzed make orbital movements or reciprocal movements on a substantially same orbit.
In a Time of Flight Mass Spectrometer (hereinafter referred to as “TOFMS”), generally, ions accelerated by an electric field are introduced into a flight space having no electric field nor magnetic field, and various ions are separated by a mass number according to a flight time until the ions reach a detector. A difference in the flight time between two different ions having different mass numbers increases as the flight time increases. Accordingly, a long flight distance is preferable in order to improve resolution in the mass number. However, it is generally difficult to provide a long flight distance linearly due to limitation in a size of a device. Conventionally, various structures have been proposed to effectively increase the flight distance.
For example, in a device disclosed in Japanese Patent Publication (Kokai) No. 11-297267, an oval orbit is formed using a plurality of troidal type sector-formed electric fields, and ions repeatedly fly around the oval orbit to increase the flight distance. In a device disclosed in Japanese Patent Publication (Kokai) No. 11-135061, a closed orbit is formed in an 8-character shape to increase the flight distance. In these TOFMSs, a flight time, from when an ion starts from an ion source to when the ion arrives at a detector after flying around the orbit for predetermined times, is measured. A mass number of the ion is determined according to the flight time. The flight time increases as the number (orbital flight number) of flying around the orbit increases. Accordingly, generally, resolution in the mass number is improved as the orbital flight number increases.
In the TOFMSs, generally, the detector starts collecting data of a detection signal (ion strength signal) when the ions start from the ion source to obtain a relationship between the flight time and the ion strength signal based on the data. However, in the TOFMSs having the structures described above, when the flight number of the ions increases, the flight time becomes longer in proportion thereto. Accordingly, it is necessary to collect a large amount of the data, thereby requiring a large capacity for storing the data.
In view of the problems described above, the present invention has been made, and an object of the present invention is to provide a mass spectrometer having an orbit in a flight space so that ions repeatedly fly along the orbit several times, wherein a capacity for storing collected data is reduced.
Further objects and advantages of the invention will be apparent from the following description of the invention.